MXS-3051: Show connection TLS cipher

This tells the user whether a session is using TLS or not. Currently, only
the client TLS cipher is shown in MaxCtrl as the backend ciphers require
additional formatting.

maxctrl/lib/show.js

@@ -208,6 +208,11 @@ const session_fields = [
         path: 'attributes.idle',
         description: 'How long the session has been idle, in seconds'
     },
+    {
+        name: 'Client TLS Cipher',
+        path: 'attributes.client.cipher',
+        description: 'Client TLS cipher'
+    },
     {
         name: 'Connections',
         path: 'attributes.connections[].server',